Numerous sealant compositions are known in the literature. One of the basic patents in this field is Harlan, U.S. Pat. No. 3,239,478, which shows combinations of styrene-diene block copolymers with tackifying resins and the like to produce a wide variety of sealants and adhesives. Further, it is known that butyl rubbers can be used in a variety of adhesives, sealants and coatings. It has been known that these butyl rubber compounds do not adhere well to polar substrates, especially in the presence of water, since the butyl rubber does not form strong chemical bonds to polar substrates.
U.S. Pat. No. 3,984,369, also issued to Harlan, recognized this phenomenon and attempted to provide a sealant composition which improved the adhesive qualities of the base butyl rubber compound. This composition covers a formulation which comprised 3 to 30 weight percent of a block copolymer, 2 to 40 weight percent of butyl rubber, 10 to 70 weight percent of a plasticizing oil having a solubility parameter ranging from 6 to 8, about 1 to 50 weight percent of an adhesion promoting resin having a solubility parameter ranging from about 8 to about 12, about 1 to about 70 weight percent of an inorganic filler and about 0.01 to about 2.0 weight percent of an ultraviolet/oxidation (UV/oxidation) stabilizer or a mixture of UV/oxidation stabilizers. This composition gave better adhesion and lower melt viscosity than previously taught similar compositions by teaching the use of a primer containing a silane coupling agent. This invention had the disadvantage that the added silane coupling agent is migratory in character. In particular, for hot melt sealants, a migratory silane may be lost during processing because of its volatility at the high temperatures required for mixing and applying hot melt sealants. In hot melt sealants for insulated glass or for headlight assembly, the migratory silane may cause fogging between the panes of insulated glass or on the inside of the headlight assembly. In certain coatings for glass bottles, the migratory silane may cause an odor which is objectionable. In coatings for electrical components the migratory silane can cause excessive corrosion.
U.S. Pat. No. 4,113,914 to Doss claims a process for applying a sealing composition to at least a portion of an area between two surfaces wherein the composition comprises:
(a) 100 parts by weight of a block copolymer selected from the group consisting of: aa. polymers of the structural formula (S----D).sub.m Y, bb. polymers of the structural formula (S----D').sub.n Y, and cc. polymers of the structural formula S----D'----S, wherein S is a block of polymerized styrene, D is a block of polymerized butadiene or isoprene, D' is a hydrogenated block of polymerized butadiene or isoprene, Y is a residue of a polyfunctional coupling agent or of a polyfunctional initiating agent, m is an integer of about 2, n is an integer of 2 or more, the block copolymer having a weight average molecular weight of 200,000 to 750,000 for polymers aa., 50,000 to 500,000 for polymers bb. and cc., PA1 (b) 1 to 30 parts by weight of an epoxy resin, PA1 (c) 10 to 250 parts by weight of a modifying resin, PA1 (d) 25 to 250 parts by weight of a filler. PA1 said polymer component comprising an A'B' block copolymer, a multiblock copolymer having at least two end blocks A and at least one midblock B, or blends of an A'B' block copolymer and the multiblock copolymer wherein: PA1 the A' and A blocks comprise monoalkenyl arene blocks and the B' and B blocks comprise substantially completely hydrogenated conjugated diene polymer blocks, and the average molecular weight of the A and A' blocks is greater than the minimum molecular weight needed to obtain microphase separation and domain formation of the A and A' blocks, and is less than the maximum molecular weight which would render the polymer incapable of being melt processed, PA1 the multiblock copolymer comprises a monoalkenyl arene content which is no more than the maximum weight percent needed to retain a modulus suitable as a sealant in the resultant composition and no less than the minimum weight percent needed to obtain the desired phase separation and the desired cohesive strength;
The application also claims an article produced in accordance with the process claimed. This process for applying the sealant and the subsequent article produced using the process involves a sealant composition with hydrogenated styrene diene block copolymers and the use of an organosilane coupling agent for improving the adhesion of the sealant to glass after water immersion. Like the composition taught by Harlan in U.S. Pat. No. 3,984,369, this added silane coupling agent is also migratory in character and for hot melt sealants, the migratory silane may be lost during processing because of its volatility at high temperatures which is required for mixing and applying the hot melt sealants. Additionally, like the sealant of U.S. Pat. No. 3,984,369, the low flash point of the migratory silane may prohibit its use in some hot melt applications because of safety considerations, including a fire hazard.
U.S. Pat. No. 4,296,008, issued to St. Clair et al claims essentially the basic sealant composition for which the instant invention is an improvement. In '008, St. Clair et al claim a formulation which contains about 0.1 to about 10 parts of a silane coupling agent. This silane coupling agent is not bound covalently to the block polymer and therefore is migratory in character. The instant invention is intended to provide a sealant composition with a silane grafted polymer component which eliminates the need for a migratory silane coupling agent.
A novel sealant composition has now been discovered which avoids the problems produced by the migratory silane.